Functional Analysis of Photosystem II

Abstract

SummaryThe structural and functional analysis of the Photosystem II complex has been facilitated by the use of model organisms which are amenable to experimental manipulation. The unicellular alga, Chlamydomonas reinhardtii, was initially chosen as a model organism based on the relative ease with which Photosystem II mutants could be generated and characterized. Furthermore, cells grown in the dark (heterotrophically) were demonstrated to synthesize chlorophyll, and assemble Photosystem II complexes which were competent for charge separation and photoactivation of the water splitting complex. These traits proved to be particularly useful for the phenotypic characterization of mutants susceptible to photoinhibition.With the recent development of chloroplast and nuclear DNA transformation technologies, however, it has been possible to engineer genes encoding polypeptides of the Chlamydomonas Photosystem II complex. As a result of these developments Chlamydomonas has become the dominant model system for genetic manipulation of the eukaryotic Photosystem II complex.In this chapter we describe the structure and primary processes of the Photosystem II complex with emphasis on results obtained from Chlamydomonas. Models for the organization of the Chlamydomonas reaction center, core, and thylakoid membrane Photosystem II complexes are presented. These models are discussed in the context of the partial reactions which each Photosystem II complex type is capable of supporting, both in wild type and mutant cells. Finally, comparisons are drawn between Chlamydomonas (eukaryotic) and cyanobacterial (prokaryotic) Photosystem II mutants of similar genotypes. It is evident from these studies that the two Photosystem II reaction center types are similar but not identical in structure and function.